I don't see it, maybe I'm just misunderstanding you. The worth of the mortgages currently for people that are being foreclosed on is zero.
Yes, but they are not the ones bearing the risk...the banks carry the risk. A foreclosed home is worth precisely what the bank can auction it off for.
If banks are not legally allowed to foreclose homes, the risk of giving out mortgages, and the risk of buying mortgage-backed securities, increases dramatically. Since there is no way to foreclose on defaulting debtors, there is serious risk of never recouping the value of the loan.
In our information-age economy, this risk is allotted and priced via hedging...and so the government is effectively setting an artificially high minimum price on mortgage-backed securities (which are
still seriously volatile).
Any student of microeconomics can tell you how severely de-facto price controls damage the economy. The government, in order to "protect" homeowners, would be setting us up for ANOTHER 2008-esque crash. Further, this will seriously reduce banks' ability to issue mortgages, which will send our already-battered real estate market into a tailspin.
These hidden dynamics are what wreck economies, but they are not readily visible to policymakers and voters.